A new update has been made to the Google webmaster guidelines document, which describes you should not block the Google ads destination URL with your robots.txt file.
The new text is under the technical guidelines and reads:
The guideline before somewhat implies the complete opposite:
So what do you make of this new change to the Google webmaster guidelines?
This was spotted first by Menashe Avramov.
Forum discussion at Google+.
Update: The following day, Google has removed the language from the guidelines. I guess they decided it was confusing also?